Cities worldwide are facing significant water-related challenges, including urban water runoffs, flooding, reduced water quality and severe water scarcity—exacerbated by rapid urbanisation and more frequent extreme weather events. On top of this, urban water runoff continues to be a major cause of water pollution in urban areas, carrying trash, bacteria, and other pollutants through gutters and stormwater systems into local waterways, typically without treatment.

City governments can pursue a “sponge city” approach by redesigning the urban fabric and integrating blue and green infrastructure (BGI) (e.g. rain gardens, permeable pavements, storage ponds, etc.) along traditional grey infrastructure (e.g. pipe networks, storage tanks, flood walls). This can help to absorb, store, filter and purify these water flows, in turn replenishing aquifers, reducing the need for expanding grey water management and minimising flood risk, while also reducing the heat island effect.

Cities can do so by, for example, integrating requirements for BGI into municipal urban planning rules for newly built up areas of city districts, industrial parks and development zones, and integrating sponge city building requirements into municipal urban planning rules. Then, local governments could also strengthen collaboration between all relevant stakeholders—from real estate developers to engineers, to water-utility organisations—to identify locally relevant opportunities for sponge cities.